1. Field of the Invention
The present invention is directed to the field of chemiluminescence analyzers. More particularly still, the present invention is directed to that portion of the abovenoted field which is concerned with improving the electrical signal response and sensitivity of a chemiluminescence detector. More particularly still, the present invention is concerned with a technique and apparatus for improving the electrical operation of a light sensing device used to sense illumination produced by a chemiluminescent reaction while simultaneously and concomitently improving the conditions of the reaction to thereby promote the chemiluminescence producing reaction.
2. Description of the Prior Art
The U.S. Pat. Nos. RE 28,374 and RE 28,376 in the names of Colvin et al. and Warnick et al. respectively, describe a Chemiluminescent Instrument and Chemiluminescent Process, respectively. It has been determined that the electrical output signal produced by a chemiluminescence detecting and/or analyzing instrument, as generally described in the aforenoted reissue patents, can be improved if the signal-to-noise ratio of the electrical light sensing means be increased. The light sensing means is typically a photomultiplier. While photomultipliers are known having large signal-to-noise ratios, they are very expensive. In order to use the less expensive light sensing means, it has been the practice to reduce the temperature of the light sensing element, and particularly the cathode of the photomultiplier used as the light sensing element. Accordingly, it has been the prior art practice to provide thermal insulation for the photomultiplier reaction chamber assembly to insulate that assembly from ambient temperature and to further provide cooling for the assembly. One form of assembly cooling has been a thermoelectric heat pump. According to the prior art, the heat extracted from the assembly is rejected to the ambient environment. This approach has successfully reduced the operating temperature of the light sensing means. However, the lowering of the temperature of the light sensing means has required that the viewing window of the reaction chamber be thickened. This has been necessitated to prevent detrimental reduction of the temperature of the reaction chamber. It has also resulted in a decrease of the light energy received by the light sensing means.
A further problem which has been encountered in the prior art is the occurrence of vapor condensation within the reaction chamber and particularly on the viewing window. This problem is a result of the dew point of the sample gas being very close to normal ambient room temperature. This problem has been aggravated by the cooling of the photomultiplier and reaction chamber assembly below the ambient temperature.
I have determined that the quantity of light generated within the chemiluminescent reaction chamber portion of such an assembly is less than one would expect under identical gas flow conditions with apparatus which does not cool the reaction chamber/photomultiplier assembly. It is therefore an object of the present invention to provide an improved cooling apparatus for cooling the light sensing element of a chemiluminescence detection instrument which does not adversely affect the generation of light in the chemiluminescent reaction chamber. It is a further object of the present invention to provide a method and apparatus for cooling the light sensing element in a chemiluminescence detection instrument which does not cause a lowering of the temperature of the chemiluminescent reaction chamber. It is a still further, and a particular, object of the present invention to provide a method and apparatus for cooling the light sensing element of a chemiluminescence instrument which will permit the chemiluminescent reaction chamber to be operated at a temperature which is higher than the temperature of the light sensing element. More particularly still, it is a principal object of the present invention to provide a method and apparatus for cooling the light sensing element of the chemiluminescence detection instrument while providing simultaneous heating of the chemiluminescent reaction chamber.